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As well as a four-wheeled vehicle, in the field of motorcycle, development of the CO2 reduction technology and practical use are required for global environment.

Zinc dialkyldithiophosphate (Zn-DTP) type additives are widely used for engine oil formulations. However, phosphorus compounds are environmental load materials. The reduction of the quantity of phosphorus compounds in engine oils is required to reduce poisoning of three-way catalysts used to purify exhaust gases from internal combustion engines.

Ito1) reported that they developed a sulfur-based additive as a substitute for Zn-DTP. Their non-phosphorus engine oil formulation for four-wheeled vehicles with a sulfur-based additive was examined to evaluate its anti-wear performance using the following test methods: JASO M328 for gasoline engines (KA24E) and JASO M354 for Diesel engine (4D34T4).

Last year, we2) reported that new concept motorcycle engine oil with this sulfur-based additive as Zn-DTP substitute was examined to meet requirements for motorcycle engine oil. The anti-wear performance, antioxidant performance, heat resistance, clutch friction characteristic and engine test were evaluated. The candidate oil showed equal or better anti-wear performance, antioxidant performance, heat resistance and clutch friction characteristic than that of engine oils containing Zn-DTP. Additionally, 600cm3 motorcycle gasoline engine bench-test had been carried out to evaluate the durability performance of that candidate oil. The better detergency of that oil, especially in the piston parts and cylinder area characterized its excellent performance than engine oils containing Zn-DTP.

To expand the application of this new concept motorcycle engine Oil with sulfur-based additive, additional evaluation has been carried out under the lower temperature and higher temperature conditions, especially for the anti-wear performance and the clutch material friction characteristics to meet motorcycle engine oil requirements.

In this study, we evaluated the effect to the anti-wear performance of the combination of sulfur-based additive and phosphorus compound, and also evaluated the effect of nitrogen-based additive to the clutch friction characteristics.

New candidate oils composed of the combination of sulfur-based additive and phosphorus compound and nitrogen additives showed better anti-wear performance under the low and high temperature condition and equal clutch friction performance with engine oil containing Zn-DTP.